1. Field of the Invention
The present invention relates to a color cathode ray tube and, more particularly, to a support member which suspends a shadow mask assembly, which has a shadow mask and a mask frame for supporting the shadow mask, at the diagonal portions of the inside of a face panel of a color cathode ray tube.
2. Background of the Invention
A color cathode ray tube of a shadow mask type has electron beams emitted from an electron gun which pass through apertures of the shadow mask to land on R, G and B pixels, respectively, on a phosphor layer.
However, part of the electron beams pass through the apertures of the shadow mask and the rest strike the inner surface of the shadow mask so as to heat it. As a result, the shadow mask is thermally expanded and domes out, such that the position of the apertures is changed against the electron beam. Thus, a demand for compensating the change is proposed.
As a conventional method of solving the doming of the shadow mask, support members called corner springs are interposed between stud pins installed at a predetermined position of the inside of a panel and a mask frame for supporting the shadow mask so as to compensate the changed position of the apertures caused by the doming.
The corner springs are installed at the center portions of the panel sides or at the corners of the long and short sides of the frame. A structure having corner spring installed on the corners of the frame has the advantage of suppressing the free vibrations of the frame.
For example, U.S. Pat. No. 4,827,180, particularly FIG. 3, discloses a shadow mask assembly suspended by four support members on the four corners of the substantially rectangular panel. Each support member has a V-shape constructor and includes a first arm portion, a second arm portion and a folded portion connecting the first and second arm portions with each other.
This shadow mask assembly has several advantages. First, when the tube operates and the temperature of the mask frame is increased, the first and second arm portions are both deformed to a flat plate, and this deformation absorbs the expansion of the mask frame. Consequently, the mask frame does not move toward the phosphor layer. Therefore, the position of the apertures does not change, and the electron beam correctly lands on the aimed phosphor pixel. Second, since the substantially rectangular mask frame is suspended by its four corners, the influence of deformations of the mask frame is smaller in comparison with a shadow mask assembly in which the mask frame is suspended by the center portions of the panel side. This can reduce the electron beam's tendency to misland on phosphor elements.
The attaching and detaching of the shadow mask assembly which is repeated many times is required to form the phosphor layer during the manufacturing process of the color cathode ray tube. At this point, in the case where the unevenness of the inside wall of the panel is severe, as shown in FIG. 5, the attachment section 511 of the first arm portion 51 is forced by force P and this force P acts as twist force P' to deform the first arm portion 51. In this case, if the calcination process for thermally removing all alien substances of each phosphor layer and panel is initiated, the support member 50 having a self-elastic force is thermally changed and tends to return to its original configuration, whereby folded portion 54 connecting the first and second arm portions with each other is forced by twisting force P". Accordingly, the mask frame suspended on the securing section of the second arm portion of the support member rotates by the deformation of the second arm portion. As a result, the initial position setting value of the shadow mask is changed, thereby deteriorating the purity of the color cathode ray tube.